Auto-averaging RC time constant calibration

Abstract

This disclosure relates to auto-averaging RC time constant calibration are described. An auto-averaging calibration circuit includes two capacitor branches, where capacitors in the capacitor branches, charge and discharge alternately to accommodate multiple charging cycles in one measurement cycle for measuring a RC time constant. A value of RC time constant is obtained in each charging cycle. A final value of the RC time constant can be determined by averaging various values of the time constants obtained during each charging cycle.

1. A calibration circuit comprising:
 two capacitor branches, wherein each capacitor branch includes a current source, at least one capacitor and a switch; 
 a resistor branch connected to the two capacitor branches, that includes a current source that induces a reference voltage and a resistor; and 
 a counter and charge commutation control that tracks charging cycles of the capacitors as they are charged and discharged. 
 
     
     
       2. The calibration circuit of  claim 1 , wherein the capacitors are tunable capacitors that are tunable to a particular cut-off frequency. 
     
     
       3. The calibration circuit of  claim 1 , wherein the at least one capacitor of one branch is charged to the reference voltage while the at least one capacitor of the other branch is discharged to zero volts to complete a charging cycle. 
     
     
       4. The calibration circuit of  claim 1 , wherein the switches are closed before a measurement cycle to eliminate residual charges at the capacitors. 
     
     
       5. The calibration circuit of  claim 1 , wherein the counter and charge commutation control instructs the switches to open and close for a measure cycle. 
     
     
       6. The calibration circuit of  claim 1 , wherein a number of charging cycles is predetermined. 
     
     
       7. The calibration circuit of  claim 1 , wherein the calibration circuit receives from a digital control, different capacitor tuning values to compute different RC time constants. 
     
     
       8. An apparatus comprising:
 a circuit that includes passive RC components; and 
 an auto-averaging calibration circuit to calibrate RC time constants for the RC components comprised of:
 a) at least two capacitor branches, wherein each capacitor branch includes a current source, at least one capacitor, and a switch; 
 b) a resistor branch connected to the capacitor branches, that includes a current source that induces a reference voltage, and a resistor; and 
 c) a counter and commutation control that tracks charging cycles of the capacitors as they are charged and discharged; and 
 
 a digital control that controls the auto-averaging calibration circuit. 
 
     
     
       9. The apparatus of  claim 8 , wherein the passive components include capacitors to be tuned to a particular RC time constant. 
     
     
       10. The apparatus of  claim 8 , wherein the circuit includes capacitors tunable to a particular cut-off frequency. 
     
     
       11. The apparatus of  claim 8 , wherein the counter and commutation control is asynchronous. 
     
     
       12. The apparatus of  claim 8 , wherein the counter and charge commutation control computes a final value of measured time constants by taking an average of recorded time constants. 
     
     
       13. The apparatus of  claim 8 , wherein the counter and commutation control tracks a number of charging cycles completed and compares the completed cycles to a predetermined number of cycles to be completed. 
     
     
       14. The apparatus of  claim 8 , wherein the digital control checks if an RC time constant is equal to a given target value, and if the RC time constant is not equal to a given target value, the digital control sends a capacitor tuning value to the capacitors. 
     
     
       15. A method for averaging RC time constant calibration in a circuit comprising:
 specifying a number of charging cycles for at least two capacitors in a calibration circuit; 
 charging a first capacitor to a reference voltage and discharging a second capacitor, wherein the first and second capacitors are tunable to a value corresponding to a cut-off frequency value for the circuit; 
 measuring an RC time constant value of the capacitors after each charging cycle; and 
 averaging the measured RC time constant values. 
 
     
     
       16. The method of  claim 15 , wherein the number of charging cycles is included in one measurement cycle. 
     
     
       17. The method of  claim 15 , wherein the circuit is tunable to the cut-off frequency value. 
     
     
       18. The method of  claim 15 , wherein the measuring the RC time constant values is performed by measuring a time interval for the charging cycle of the capacitors, and counting the number of charging cycles that are completed. 
     
     
       19. The method of  claim 15  further comprising tracking a number of cycles completed and determining if the specified number of cycles has been completed. 
     
     
       20. The method of  claim 15  further comprising passing the averaged RC time constant values to a control that adjusts the circuit.